Experimental study on the bearing characteristics of piles under the influence of thickness of underlying karst cave roof

To study the influence of the thickness of the underlying karst cave roof on the bearing characteristics of the rock-socketed pile, the load test of the model pile under different roof thickness conditions(1<italic>D</italic>–5<italic>D</italic>) was carried out. The failure mode of the karst cave roof, the load-displacement curve, the distribution characteristics of the axial force and resistance of the pile, and the variation of the ultimate bearing capacity with the roof thickness were analyzed. The calculation model of the ultimate bearing capacity of the karst cave roof is established. Based on the roof failure mode and the H-B criterion, the calculation formula is derived. The results show that: (1) when the roof thickness is 1<italic>D</italic> and 2<italic>D</italic>, the roof punching failure; when the roof thickness is 3<italic>D</italic> and 4<italic>D</italic>, the roof is bent-pulled-punched combined failure; when the roof thickness is 5<italic>D</italic>, the roof is flexural failure; the critical thickness of the underlying karst cave roof is 5.9<italic>D</italic>. (2) The load-displacement curve of the test pile is a steep change type, and the load-displacement relationship is linear before the steep change point appears. The pile top displacement corresponding to the steep change point of the load-displacement curve is(0.215‐0.3)<italic>D</italic>. The code takes 0.05<italic>D</italic> displacement corresponding to the load as the ultimate bearing capacity of the pile is conservative. (3) For every 1<italic>D</italic> increase in the roof thickness, the ultimate bearing capacity of the test pile is significantly improved, but the increasing extent is gradually reduced from 158% to 35%. When the roof thickness exceeds 2<italic>D</italic>, the bearing ratio of the pile end exceeds 90%. (4) The proposed calculation method of the ultimate bearing capacity of the pile of the underlying karst cave is compared with the experiments. The error range of results is 3.29%‐15.62%. They are in good agreement.